Detonator actuator

ABSTRACT

An actuator for use in conjunction with a detonator for blasting comprises electronic circuitry which on receiving input signals generates an output arm signal to arm a detonator, and then after a predetermined delay an output actuate signal to fire the detonator and an associated explosive charge. The delay is capable of being remotely and precisely set. The actuator is preferably used in conjunction with a control device which has a microcomputer whose memory contains arm and actuate codes and which has both arm and actuate keys. This microcomputer is such that the actuate keys must be operated within a predetermined period after operation of the arm key, otherwise an actuate signal is not transmitted to the actuator.

This invention relates to an actuator to be used with a detonator and toa detonator-actuating system for use in blasting.

BACKGROUND ART

A conventional blasting system comprises a series of explosive chargeswhich are detonated by detonators which are wired to a remote commandsource. In order to prevent breakage of the wiring connecting detonatorsset to go off late in the blasting by earlier explosions, the detonatorsare provided with delays, such that the last detonator to explode hasreceived its firing signal prior to the explosion of the first. Recentimprovements in the system have included electronic delays (replacingthe older, less precise pyrotechnic delays), and the ability to programsuch delays in situ. German Offenlegungsschrift 3301251 provides anexample of the versatility of which these systems are capable.

There has recently been provided in my copending Australian PatentApplication Number PH1255 a detonator which comprises conditioning meanswhich renders fusehead conductors incapable of carrying a voltage orcurrent capable of firing the detonator prior to the altering of theconditioning means from a "normal" (incapable of being fired) state toan "armed" state. This provides a considerable safety factor notpreviously present in detonators.

DISCLOSURE OF INVENTION

I have now found that it is possible to maximise this safety factor byusing such detonators in combination with a particular actuating system.I therefore provide, according to the present invention, an actuator fora detonator, characterised in that the actuator comprises controlcircuitry which is responsive to input signals from the control deviceapplied to inputs thereof, said control circuitry being operable, onreceipt of at least one predetermined input signal, to (i) generate anoutput arm signal which is applied in use to the detonator and render itcapable of being actuated and (ii) generate an output actuate signalwhich is applied to the detonator after a predetermined delay relativeto said predetermined input signals to cause explosive actuation of thedetonator.

By "actuator" I mean a unit whose function is to receive signals from acontrol device, and to actuate a detonator. The type of detonator withwhich an actuator of the type used in this invention is associated maybe one which must be armed before it can be detonated. An especiallypreferred type is described in my co-pending Australian PatentApplication No. PH1255. However, the actuators according to my inventionmay be used in association with conventional detonators by, for example,connecting the detonator with the actuator such that only the actuatesignal is transmitted to the detonator. By "associated", I mean that thedetonator and the actuator may be connected in some way such thatsignals may be passed from actuator to detonator. This may be achieved,for example, by wiring the two components together, or by incorporatingthe actuator within the detonator. However, in a preferred embodiment,the actuator and detonator are in modular housings, and are simplyconnected together prior to putting into a blasthole. In this case, allthe appropriate electrical connections are made by the connection of themodular housings.

The actuator for use in this invention incorporates the delay which isso important in large-scale commercial blasting. The specific length ofdelay may be built into the actuator during manufacture, but I prefer tohave the delay programmable; this confers considerable versatility onthe system. Thus, an actuator may be programmed electronically prior toits being inserted in a blasthole. Even more versatility is conferred byhaving the actuator programmable when the detonator is in place in theblasthole via the means through which the input signals are transmitted.Thus, a blast pattern can be altered at will and in complete safety upto the time of sending of the input arm and input actuate signals.

The electronic circuitry within the actuator stores delay informationand acts on an appropriate signal or appropriate signals from thecontrol device to generate output arm and output actuate signalsseparated by a selected delay time. Preferably, the circuitry willcomprise a microcomputer with a memory which stores at least both an armcode and an actuate code and preferably also the selected delay time.The microcomputer analyses input signals, and when it identifies apredetermined signal or predetermined signals it then causes to begenerated appropriate corresponding output arm and actuate signals.

The nature of the signal received by the actuator may be any suitablesignal known to the art. It may be, for example, a single signal, andthe circuitry of the actuator may be such that this signal can cause thegeneration, by reference to the arm and actuate codes and thepredetermined delay stored in the actuator circuitry, of both arm andactuate signals, separated by a predetermined delay. A typical signal ofthis type is a voltage which is in excess of a predetermined level.Other signals may comprise both an arm code and an actuate code, forexample, a voltage step signal wherein the leading edge of the signalcomprises an arm signal and the trailing edge an actuate signal. Iprefer, however, that both arm and actuate signals be digital signals.This has a number of advantages. It means that if the actuator isconditioned to recognise certain digital codes, it will act only onthose codes. Accidental or unauthorised firing can thus be almostcompletely eliminated.

The nature of the signal or signals transmitted by the actuator to thedetonator may be any convenient signal suitable for the purposes ofactuating the detonator. In the case of a conventional detonator, it maybe a simple voltage or current suitable for causing the ignition of aflashing mixture and the consequent explosion of the detonator. However,the signal preferably comprises a multi-bit digital code; when such asignalling system is used with a preferred detonator as described in myco-pending Australian Patent Application No. PH 1255, it permits ofdegrees of security and safety not attainable with known detonatingsystems.

The power to drive the actuator and the detonator itself may be providedby an convenient means, consistent with the fact that a detonator set toexplode late in a series of blasts should not be prone to failure by thebreakage by an earlier explosion of a wire connection thereto. The powersource for the arming and actuating of the detonator should therefore bein close proximity to the actuator and preferably either enclosed withinthe actuator housing or capable of being connected to it. The powersource may be a battery, or preferably a temporary power source such asa capacitor which is charged by signals from the surface. In anespecially preferred embodiment of my invention, the capacitor is housedin a separate modular unit which can be attached to the detonator andactuator units, such that they form an integral unit with internalwiring and connections appropriately joined by the act of joiningtogether the individual modular units.

The actuator receives its signals from a control device on the surface.This may be a remote exploder box of the type well known to the art.However, when the actuators of my invention are used in conjunction witha selected control device, the result is a detonator actuating system ofremarkable versatility and safety. I therefore also provide a detonatoractuating system comprising

(a) an actuator as hereinabove described associated with a detonatorwhich has an explosive charge; and

(b) a control device for controlling by means of signals to the actuatorthe operation of the detonator.

the system being further characterised in that the control devicecomprises a microcomputer having a memory which stores at least an armcode and an actuate code, and wherein the microcomputer has an arm keywhich upon actuation by a user causes generation and emission to theactuator of an arm signal derived from the arm code, and an actuate keywhich upon actuation by a user causes generation and emission of anactuate signal derived from the actuate code, the microcomputer beingsuch that the actuate key must be actuated within a predetermined periodafter actuation of the arm key otherwise the actuate signal is nottransmitted to said actuator.

My invention additionally provides a control device suitable for use ina detonator actuating system as hereinabove described, and a method ofblasting using such a system.

The control device which acts in concert with the actuator is adapted tocontrol a plurality of detonators. It comprises a microcomputer with atleast arm and actuate codes, and arm and actuate keys which, whenoperated, act to generate arm and actuate signals and send them to theactuator. The microcomputer is such that the actuator key must beoperated within a predetermined period after operation of the arm key,otherwise no actuate signal is transmitted. This feature adds a furtheruseful margin of safety to an already very safe system.

Preferably the memory additionally stores a reset code and themicrocomputer operates to generate an output reset signal derived fromthe reset code if the actuate key is not actuated within thepredetermined period after actuation of the arm key, the output resetsignal rendering the detonators incapable of being explosively actuateduntil a predetermined sequence of output arm and actuate signals isreceived. It follows of course, that the actuator must have appropriatecircuitry which permits of this resetting function.

In a further preferred embodiment, the delay of the actuator unit may becalibrated from the control device. This may be achieved by having anactuator unit which is responsive to calibrate signals and themicrocomputer of the control device is arranged to generate an outputcalibrate signal in response to actuation of a calibrate key or aprogrammed instruction whereupon timing means in the control circuitryof the actuator unit is actuated for a period terminated by a controlsignal from the control device, the output of the timing means beingstored in the control circuitry whereby a delay period stored thereincan be calibrated on a time basis relative to the control device. It ispossible to incorporate the calibration function in the control devicesuch that it is automatically carried out when the arm key is operated.

As hereinabove stated, it is possible not only to calibrate the delaytimes for accurate detonation but also to program them from the surface.This can be done from a suitably equipped control device. A furtherconsiderable advantage of my invention is that the calibration may becarried out only seconds before the actual blast, and the calibrationsignals may be part of the blast signal itself. This allows the use oflow-cost components and reduces costs considerably.

In one preferred embodiment of my invention, the actuator may beequipped with a transducer unit which is couplable thereto such that allthe appropriate electrical connections are made by the coupling. As iswell known in the art, a transducer is an electronic device which isresponsive to a preselected physical parameter (for example, pressure ortemperature) and which produces corresponding condition signals whichmay then be sent, for example, to a measuring instrument or to anapparatus affected by the parameter so as to modify its behaviour. Inthis case, information from a transducer may be used to vary thecalibration of the actuator, and any variation is communicated back tothe control device at the surface, which control device is capable ofreceiving such signals. The actuator can thus "talk back" to the controldevice and this permits much tighter control over blasting operations.

In some embodiments, the control device may include a connector whichenables direct connection with the control circuitry of the actuatorunits so as to read data stored in the actuator unit. That data mightfor instance comprise an identity code of the user, a code numberassigned to a particular blast, and the delay period programmed into thedetonator control circuitry. The control device may include a displaysuch as an LCD display or a VDU for displaying this information to theuser. In a further embodiment of my invention, the detonators may bereceptive to control signals which prevent them from operating, and thecontrol device may comprise circuitry which sends to the detonators acontinuous stream of control signals which prevents any accidental orinadvertent firing. Suitable circuitry is described in my co-pendingAustralian Patent Application No. PH1258.

The invention will now be further described with reference to thefollowing drawings:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a quarry having a plurality of chargesarranged to be activated by remote control;

FIG. 2 is a similar view but showing an arrangement in which the chargesare set off by a direct wire connection;

FIG. 3 is a side view of a detonator assembly;

FIG. 4 is a schematic sectional view through the detonator assembly ofFIG. 3;

FIG. 5 is a schematic view of lines in a communication bus;

FIG. 6 shows the circuitry of one embodiment of a conditioning meansaccording to the invention;

FIG. 7 shows the circuitry of another embodiment of a detonator unit;

FIG. 8 is a schematic circuit diagram for an embodiment of a detonatoractuator unit;

FIG. 9 is a connection table showing the connections of the componentsof FIG. 8;

FIG. 10 is a flow diagram illustrating the operation of the detonatoractuator unit of FIG. 8;

FIG. 11 is a schematic circuit diagram for another embodiment of adetonator actuator unit;

FIG. 12 is a connection table showing the connections of the componentsof FIG. 10;

FIG. 13 is a schematic circuit diagram for an embodiment of a transducerunit;

FIG. 14 is a flow diagram for the operation of a transducer programme;

FIG. 15 is a schematic circuit diagram of part of a detonatorcontroller;

FIG. 16 is a connection table showing the connections of the componentsof FIG. 15.

FIG. 17 is a flow diagram illustrating the operation of the controller;

FIG. 18 is a sectional view through an embodiment of a detonatorassembly;

FIG. 19 is a schematic circuit diagram for an embodiment of a detonatoractuator unit suitable with assemblies as shown in FIG. 18;

FIG. 20 is a connection table showing the connections of the componentsof FIG. 19;

FIG. 21 is a flow chart illustrating the operation of the circuit shownin FIG. 19;

FIG. 22 is a schematic circuit diagram for an embodiment of a detonatoractuator unit;

FIG. 23 is a connection table showing the connections of the componentsof FIG. 22.

FIG. 24 is a flow diagram illustrating the operation of the detonatoractuator circuit shown in FIG. 22.

MODES OF CARRYING OUT THE INVENTION

FIG. 1 shows a quarry face 2 and a number of charge holes 4 drilled intothe ground behind the face. A detonator assembly 6 is located in eachhole 4 and the remainder of the hole is filled with a bulk charge 8 suchas ammonium nitrate fuel oil mixture which is supplied as a powder orslurry, in accordance with known practice. The detonator assemblies 6are connected by conductors 10 to an antenna 11 for a radio transceiver12 located in one or more of the assemblies 6. The transceiver 12receives control signals from a controller 14 via a transceiver 15 sothat the detonator assemblies can be actuated by remote control. A sitesafety unit 16 may also be provided to provide additional safety duringlaying of the charges. The unit 16 is preferably located near theantenna 11 so as to be likely to pick up all signals received by theantenna 11. The safety unit 16 includes a loudspeaker 18 which isoperated in emergency conditions and prior to a blast. The detonatorassemblies 6 are arranged to be actuated at an accurately determinedtime after the controller 14 has transmitted signals for the blast tocommence. The detonator assemblies 6 can be arranged to be activated ina precisely defined time sequence so that efficient use is made of theblasting materials. The number of blast holes 4 can of course be veryconsiderable. For instance, in some large scale mining and quarryingoperations up to 2000 holes are sometimes required in a single blastingoperation.

FIG. 2 shows an arrangement which is similar to FIG. 1 except thatcommunication from the controller 14 to the detonator assemblies 6 isvia a wire 20 extending from the controller 14 to the conductors 10. Inthis case the safety unit 16 is not required because of the hard wireconnection between the controller 14 and the detonator assemblies 6, butit could be coupled to the wires 20 so as to sound an alarm when signalsare detected for causing actuation of the detonator assemblies.

FIG. 3 shows the detonator assembly 6 in more detail. As will bedescribed hereinafter, it comprises a number of interconnected moduleswhich can be varied in accordance with requirements. In the illustratedarrangement the modules comprise a detonator unit 22, an actuator unit24, a transducer unit 26, a battery unit 38, an expander unit 40 and aconnector unit 42. The units themselves can be made with variousmodifications as will be explained hereinafter. Generally speakinghowever a detonator assembly 6 in a useful configuration will include atleast the following units: a detonator unit 22, an actuator unit 24, abattery unit 38 and a connector unit 42.

FIG. 4 shows a longitudinal cross section through the detonator assembly6 revealing in schematic form the physical layout of the components.

The detonator unit 22 comprises a tubular housing 44 which for instancemight be formed from aluminium, or a resilient material which is aconductor such as carbonised rubber. The housing 44 is provided withtransverse partitions 46 and 48 press fit into the housing 44. A firstchamber 50 is formed between the partitions 46 and 48 and a secondchamber 52 is formed between the partition 46 and the closed end wall 54of the housing. Extending into the second chamber 52 are two fuseheadconductors 56 and 58 separated by an insulating block 60. The conductors56 and 58 are connected to a fusible element 62 located within aflashing mixture charge 64. The remainder of the second chamber 52 isfilled or partly filled with a base charge 66 of explosive material. Theconductors 56 and 58 include insulated portions 68 and 70 which extendthrough an opening 72 in the partition 46 and into the first chamber 50.

Located within the first chamber 50 is a circuit board 74 which mountselectronic and/or electric components. The board 74 is supported by tabs76 and 78 pressed from the partitions 46 and 48. The partition 48 alsosupports a multiport connector 108 for a bus 82.

The bus 82 has multiple lines which enable electrical interconnection ofthe various modular units although not all of the lines are required forthe functioning of particular units. FIG. 5 shows schematically thevarious lines in the bus 82 for the illustrated arrangement. In thiscase there are 11 lines 84, 86, 88, 90, 92, 94, 96, 98, 100, 102 and104, some of which are required for the operation of the circuitry onthe board 74 of the detonator unit 22.

FIG. 6 illustrates diagrammatically a circuit 106 which is mounted onthe board 74 of the unit 22. The circuit 106 includes a connector 108which allows connection to selected lines in the bus 82. In theillustrated arrangement, the line 84 is a voltage supply line and theline 86 is a ground line for the supply. The lines 94 and 96 carry, atappropriate times, high currents which enable fusing of the fusingelement 62. The line 104 carries clock pulses whereas the line 102carries an ARM signal which places the detonator unit 22 in a "armed"state so that it can be activated on receipt of appropriate drivingcurrents on the lines 94 and 96. In the illustrated arrangement, thesignals and currents on the lines 94, 96, 102 and 104 are derived fromthe actuator unit 24. The power supply lines 84 and 86 are coupled toreceive power from the battery unit 38.

The circuit 106 includes a relay 110 having a driving coil 112, normallyclosed contacts 114 and normally open contacts 116 which are connectedto conductors 113 and 115 which are connected to the lines 94 and 96 viaconnector 108. The normally closed contacts 114 are connected by meansof conductors 117 to the aluminium housing 44 so that both sides of thefusible elements 62 are shorted directly to the housing. This is animportant safety factor because the detonator unit 22 cannot beactivated unless the relay 110 is operated. This protects the unit 22from unwanted operation caused by stray currents or radio frequencyelectromagnetic radiation. In the illustrated arrangement, the relay 110is not operated until just before signals are delivered to the lines 94and 96 for activation of the detonator unit. The arrangement thereforehas the advantage that until just prior to when the detonator unit 22 isactivated, the fuse head conductors 56 and 58 cannot receive anyelectromagnetic or electrostatic charges which might inadvertently fusethe element 62.

The operating coil 112 of the relay is connected to a logic circuit 118which receives input from lines 102 and 104. The preferred arrangementis that the circuit 118 must receive an ARM signal comprising a two partfour bit code on the line 102 in order to produce an output on line 120which activates the relay.

The circuit 118 includes a 74164 eight bit shift register 122 havingeight output lines Q₀ -Q₇. The circuit further includes four exclusiveOR gates 124, 126, 128 and 130 connected to pairs of outputs from theshift register 122. The outputs of the exclusive OR gates are gated in afour input AND gate 132, the output of which is in turn connected to oneinput of a three input high current AND gate 134. The circuit furtherincludes a four input NAND gate 136 connected to the first four outputsof the register 122 and a second NAND gate 138 connected to the secondfour outputs of the register 122. The outputs from the NAND gates 136and 138 are connected to the remaining two inputs of the AND gate 134.The configuration of the gates connected to the outputs Q₀ -Q₇ of theregister 122 is such that only selected eight bit signals on the line102 will cause a signal to appear on the output 120 for activating therelay. The signal must be such that the first four bits are exactly thecomplement of the second four bits and further the first four bitscannot be all 1's or all 0's. The latter requirements are important inpractice because it prevents erroneous operation of the circuit 118 inthe event that a circuit fault causing a high level or short circuit tobe applied to the line 102. The circuit 106 illustrated above is givenby way of example only and it would be apparent that many alternativecircuits could be used. If at any time a signal is received on line 102which is not an ARM signal the output line 120 will go low anddeactivate the relay 110. The controller 14 may generate RESET signalsfor this purpose. In any event the logic circuitry 118 will cause theoutput 120 to go low if any signal other than an ARM signal is received.The following are examples of valid ARM signals

    00011110

    10000111

    01001011.

Further, the circuit 106 could be integrated if required, except for therelay.

FIG. 7 illustrates an alternative circuit 140 for the detonator unit 22.The inputs from the bus 82 to the connector 108 are the same as for thecircuit 106 and the logic circuitry 118 is also the same as for thecircuit 106. An alternative arrangement is however employed to ensurethat the lines 94 and 96 are not electrically connected to the fusibleelement 62 until just prior to actuation on receipt of a correctly codedsignal to the logic circuitry 118. In this arrangement, the circuitincludes two solid state relays 142 and 144. The relays have electrodes146 and 148 which are permanently connected to ground. The relaysinclude electrodes 150 and 152 which are connected to the insulatedportions of the conductors 56 and 58 leading to the fusible element 62.The relays are such that the electrodes 146 and 150 and the electrodes148 and 152 are internally connected so that both conductors 56 and 58are grounded and connected to the housing 44. The relays includeelectrodes 154 and 156 which are connected to the lines 94 and 96 viaconductors 113 and 115. When the relays receive triggering signals ontrigger electrodes 158 and 160 the internal connections change so thatthe electrodes 150 and 154 and the electrodes 152 and 156 are internallyconnected. In this case the conductors 56 and 58 are no longer groundedand are electrically connected to the lines 94 and 96 in readiness foractivation of the fusible element 62. Triggering of the relays dependsupon the output line 120 from the logic circuitry 118 as willhereinafter be explained.

The output line 120 from the circuitry 118 is connected to the input ofan amplifier 162 which is connected to the junction 164 of three fusiblelinks 166, 168 and 170 via a resistance 172. The circuit includes an ANDgate 174 one input of which is connected to the output line 120 and theother input of which is connected to the junction 164. Output from thegate 174 is connected to the trigger terminals 158 and 160 of therelays. The arrangement is such that during normal operation both inputsto the gate 174 are low so that the relays are not triggered. Whenhowever a correctly coded signal is present on the line 102, the outputline 120 of the circuitry 118 will go high to a sufficient extentwhereby the fusible links 164, 166 and 168 will rupture. When all linkshave been ruptured the junction 164 will be high and hence the gates 174will go high and the relays will be triggered. This couples theconductors 56 and 58 to the lines 94, 96 in readiness for actuation. Itwill be appreciated that until the logic circuitry 118 detects acorrectly coded signal, the fusible element 62 is protected by thefusible links 166, 168 and 170. The arrangement prevents inadvertentcharges or currents being developed in the conductors 56 and 58 due tostray electromagnetic or electrostatic fields.

The detonator actuator 24 illustrated in FIGS. 3 and 4 includes atubular housing 176 preferably formed from aluminium. The unit includespartitions 178 and 180 which define a chamber 190 in which a circuitboard 192 for electric and/or electronic components are mounted. Theboard 192 is supported by tabs 194 and 196 pressed from the partitions.The bus 82 extends through the chamber 190 and is connected at eitherend to connectors 198 and 200. One end of the housing 176 is formed witha keyed reduced diameter spigot portion 202 which in use is received inthe free end of the housing 44 of the detonator unit 22. The arrangementis such that when the spigot portion 202 is interlocked with the housing44 the connectors 198 and 108 establish appropriate connections for thevarious lines of the bus 82. The actuator unit 24 may include an LED 204which can be mounted so as to be visible when illuminated from theexterior of the actuator unit 24.

The actuator unit 24 performs a variety of functions in the detonatorassembly 6. Generally speaking, it ensures that the detonator unit 22 isactuated only in response to correctly received signals from thecontroller 14 and at an exactly defined instant of time. Other functionsof the actuator unit 24 are to ensure correct operation of the otherunits in the assembly on interconnection of the various units and tocontrol the operation of the transducer unit 26.

FIG. 8 shows in schematic form one arrangement for the circuitry 206mounted on the board 192 in the actuator unit 24. The circuitry 206generally speaking includes a microcomputer with memory to storeprogrammes and data for correct operation of the unit 24 as well as theother units of the assembly. The data includes data relative to theprecise delay required for actuation of the detonator unit 22 followinggeneration of a blast commence signal (or BOOM command) from thecontroller 14. Further, the stored programme provides for calibration ofa crystal clock in the circuitry 206 by the controller 14 just prior tooperation. This ensures a high level of accuracy of all the time basedfunctions of the assembly 6 which is therefore not dependent uponaccurately selected components in the circuit 206. Further the accuracywould not be influenced by temperatures and pressures in the blast holes4 at a blasting site.

The circuit 206 includes an 8085 CPU 208, an 8155 input/output unit 210,a 2716 EPROM 212, a 74123 monostable retriggerable multivibrator 214 anda 74377 eight bit latch 216. The components are connected together asindicated in the connection table (FIG. 9) SO as to function as amicrocomputer, as known in the art.

FIG. 10 shows schematically a flow chart of some of the programmefunctions which are carried out by the microcomputer 206. When power issupplied to the circuit by connection of the battery unit 38 in thedetonator assembly 6 a power supply voltage and ground are establishedon the lines 84 and 86. The multivibrator circuit 214 ensures that theCPU 208 is reset on power up. The first programming function performedby the microcomputer is to ensure that the detonator units 22 are madesafe. This is accomplished by sending eight consecutive zeros from pin32 of the input/output device 210, the pin 32 being connected to theline 102. This ensures that the register 122 in the detonator 22 isinitialised to zero and accordingly the unit 22 cannot be activatedbecause of the arrangement of the logic circuitry 118. This step isindicated by the functional block 218 in FIG. 10.

After initialisation, the microcomputer waits for a command from thecontroller 14 as indicated by programming step 220. Commands from thecontroller 14 are received by the connector unit 42 and are thentransmitted on the line 88 of the bus 82. The command signals on line 88preferably comprises eight bit codes in which different bit patternsrepresent different commands. Typical command signals would be for (a) arequest for information from the transducer unit 26, (b) a CALIBRATEcommand to commence calibration procedures, (c) a BLAST code for armingthe detonator units 22, (d) a BOOM command for exploding the units 22,or a RESET command for resetting the units 22. Accordingly, FIG. 10shows a question box 222 which determines whether the signal on the line88 is a request for information from the transducer unit 26. If thesignal is the appropriate signal the programme will then enter asub-routine indicated by programme step 224 to execute the transducerinterrogation and transmission programme. A flow chart for thisprogramme is shown in FIG. 14. After execution of the transducerprogramme, the main programme returns to the question box 222. Thesignal on the line 88 will then no longer be a request for informationfrom the transducer. The programme will then pass to the next questionbox 226 which determines whether a signal is on the line 88 is aCALIBRATE command appropriate for commencement of calibrationprocedures. This is indicated in the flow chart by question box 226. Ifthe signal is not a CALIBRATE command, the programme returns and waitsfor an appropriate command. Receipt of an incorrect command at any timereturns the programme to the start.

When the controller 14 transmits a CALIBRATE command, this will berecognized by the programme which then commences calibration of timingof pulses derived from the crystal clock 228 connected to pins 1 and 2of the CPU 208, as indicated by step 230 in FIG. 10. The programme thenwaits for a further signal on line 88 to stop counting of the pulses andto record the number of pulses counted. This is indicated by step 232 inFIG. 10. These programming steps enable the clock rate of the CPU 208 tobe accurately correlated to the signals generated by the controller 14and transmitted on the line 88 so that the actuator unit 24 can be veryaccurately calibrated relative to the controller 14. The controller 14can be arranged to have a precisely defined time base so that ittherefore is able to accurately calibrate a multiplicity of actuators 24which do not have accurately selected components and would therefore notnecessarily have a very accurately known time base.

Moreover, the calibration procedures can be carried out just prior todispatch of signals to activate the detonator units so as to minimizethe possibility of errors owing to changing conditions of temperatureand pressure or the like.

In the preferred arrangement, the signal on the line 88 to stop thetimer is in fact another BLAST code generated by the controller 14, theBLAST code being selected so as to be identifiable with the particularblast e.g. user identity, date, sequential blast number, etc. Thequestion box 234 in FIG. 10 indicates the required programming step. Ifthe next signal received on the line 88 is not a correct BLAST code, theprogramme returns to the start so that recalibration will be requiredbefore the detonator unit 22 can be armed.

If on the other hand the BLAST code is correct the programme thencalculates the exact delay required by the actuator 24 prior togenerating signals for explosively activating the detonator unit 22.This is indicated by the programming step 236 in FIG. 10. For instance,the actuator unit 24 may be required to actuate the detonator unit 22precisely 10 ms after a precise predetermined delay from commencement ofthe blasting sequence which is initiated by generation of a BOOM commandby the controller 14. The information regarding the particular delay isstored in the EPROM 212 and the programme is then able to calculate theexact number of clock cycles for the microcomputer 206 required to givethe precise delay. The calibration information has in the meantime beenstored in RAM within the input/output device 210.

Following this step, the actuator unit 24 may signal to the controller14 that it is functioning correctly and that appropriate signals havebeen received. Signals for transmission back to the controller 14 arecarried by line 90 which is coupled to pin 4 of the CPU 208. This isindicated by step 238 in FIG. 10. The arming of the detonator unit 22 isindicated by step 240 in which an ARM signal is generated on pins 31 and32 of input/output unit 210. The programme then is arranged to set apredetermined period say 5 seconds in which it must receive a BOOMcommand signal on the line 88 from the controller 14 for activation ofthe detonator unit 22. If the BOOM command signal is not received withinthe 5 second period, the programme returns to the start so thatrecalibration procedures etc. will be required in order to again be inreadiness for actuation of the detonator unit 22. These programmingsteps are denoted 242, k244 and 246 in FIG. 10. The BOOM command signalon line 88 must be a correct eight bit pattern of signals otherwise theprogramme will again return to the start, as indicated by the questionbox 248. If the BOOM command is correct, the required delay is retrievedfrom the RAM in the input/output unit 210 and the delay is waited, asindicated by programming steps 250 and 252. At the end of the delayperiod, a signal is passed to the input/output unit 210 the output pins29 and 30 of which go high. These output pins are connected by currentdrivers 254 and 256 to the lines 96 and 94 and the current driverssupply a fusehead actuating current, say 1.5 amps, required to fuse theelement 62 and ignite the flashing charge 64 and thus actuate thedetonator unit 22. This is indicated by the programming step 258.Actuation of the detonator unit 22 of course destroys the detonatorassembly 6 so that the controller 14 will be aware of successfuloperation of the detonator assembly by its silence. If however there hasbeen a malfunction, the programme includes a question box 260 whichdetermines whether the CPU is still functioning and if so thisinformation is communicated to line 90 for transmission to thecontroller 14. The programme then returns to the start whereupon thedetonator unit is again made safe, this being indicated by programmingsteps 260 and 262.

FIG. 11 illustrates alternative circuitry for the actuator unit 24. Inthis arrangement, the power supply lines 84 and 86 are used forcommunication from the controller 14 to the actuator assembly 6. Thesame lines may be utilised for communications in the reverse directionif a transducer unit 26 is utilised. Alternatively the line 90 may beused for that purpose if required as shown in FIG. 11. The circuit ofFIG. 11 essentially comprises a microcomputer 490 comprising and 8085CPU 492, a 2716 EPROM 494, an 8155 input/output unit 496, a 74123triggerable monostable multivibrator 498 and a 74377 eight bit latch500. These components are connected together as indicated in theconnection table (FIG. 12) so as to function as a microcomputer as isknown in the art. The principle function of the microcomputer 490 is tocarry out the programming steps indicated diagramatically in FIG. 10 aswell as FIG. 14 where a transducer unit 26 is employed.

Power supply for the detonator assembly 6 is derived from the voltageapplied to the line 84 by the controller 14 via the conductors 10 andwires 20 of FIG. 2. The voltage is stored in a storage capacitor 504.The diode 502 ensures the capacitor 504 cannot discharge itself backalong the path to pin 5 of the CPU 492, or to the controller 14 alongconductors 10 and 20. The normal level applied to the line 84 isselected to be 2.4 volts which is sufficient to charge the capacitor 504and maintain the CPU 492 but insufficient to generate a response on theinput pin 5 of the CPU 492 which is connected to the line 84. Whensignals are required to be transmitted to the assembly 6 from thecontroller, the controller is arranged to send a pulsed waveform thepeak voltages of which are say 5 volts which is above the thresholdlevel for a positive input to the pin 5 of the CPU 492. By this means,various coded signals can be sent from the controller 14 to theassemblies. The output pin 4 could be used to apply voltages to the line84 for communication from the assembly 6 to the controller, provided thetime sequencing were correctly arranged. Alternately, the output pin 4could be connected to the return communication line 90 of the bus.

Returning now to FIGS. 3 and 4, the transducer unit 26 comprises atubular housing 264 preferably of aluminium and formed with a spigotportion 266 which interlocks with the open end of the housing 176 of theactuator unit 24. The shape is such that it cannot mate with the unit22. The housing has partitions k268 and 270 which define a chamber inwhich a circuit board 273 for electronic and/or electrical components islocated. The partitions 268 and 270 can be used to support the board 273as well as supporting electrical connectors 272 and 274 for the bus 82.The housing 264 has an opening to permit access to a transducer element276 which is sensitive to surrounding temperature, pressure, humidity orother parameters as required. For temperature sensing the element 276could be bonded to the inner surface of the housing 264. The transducerunit 26 may have several transducer elements and so be responsive to anumber of different parameters. When the spigot portion 266 isinterlocked with the end of the actuator unit 24, the connector 272mates with the connector 200 so that the bus 82 extends through therespective units. In its simplest configuration, the board 273 wouldsimply carry any circuitry which might be necessary for correctoperation of the transducer element 276 and for coding of its output forapplication to lines 98 and 100 of the bus 82.

FIG. 13 shows an example of one such circuit. In this arrangement theoutput 278 of the transducer element 276 is connected to the input of avoltage to frequency converter 280 which may comprise an LM 331 circuit.The resistors and capacitors connected to the converter 280 are wellknown and need not be described in detail. Output from pin 3 of theconverter 280 is connected to the line 98 of the bus, the line 100 beingground. The frequency of the signal on the line 98 will be proportionalto the output of the transducer element 276 and thus be proportional tothe temperature pressure humidity etc. to which the element 276 isexposed. The signal on the line 98 is applied to the CPU 208 forconversion to digital form and outputted on pin 4 which is coupled toline 90 of the bus for transmission to the controller 14.

FIG. 14 shows schematically a flow chart for processing by themicrocomputer 206 of the variable frequency output signals of thetransducer unit 26. The flow chart of FIG. 14 is an example of theprogramme denoted by 224 in FIG. 10. The first step in the programme isto clear a timer, as indicated by programme step 282. The timer may belocated in the input/output unit 210. The programme then waits for therising edge of the first received pulse on the line 98, as indicated bystep 284. The programme then starts the timer and waits for a fallingedge of the same pulse, as indicated by steps 286 and 288. The timer isthen stopped and its value is indexed into a conversion table stored inthe EPROM 212, as indicated by steps 290 and 292. The programme thenlooks up the value of the parameter such as temperature, pressure, etc.and sends an appropriately encoded signal to the controller 14 via line90, as indicated by steps 294 and 296. The programme then returns to themain control programme of the actuator unit 24, as indicated in FIG. 10.

In circumstances where communication from the detonator assemblies 6 tothe controller 14 is not required, the connector unit 42 need only becapable of receiving signals from the controller 14 and does not need totransmit signals thereto. Thus, the unit 42 need only include a radioreceiver for use with radio controlled arrangements as in FIG. 1, orline connectors for use in wire systems as shown in FIG. 2.

Returning once again to FIGS. 3 and 4, the battery unit 38 comprises atubular housing 298 with a spigot portion 300 which is interlockablewith the open end of the housing 264 of the transducer unit 26. Thespigot 300 is also shaped so that it can be plugged directly into thehousing 176 of the actuator unit 24 in instances where the transducer 26is not required. The shape of the spigot 300 is such that it cannot beinserted into the open end of the housing 44 of the detonator unit 22.The unit 38 includes partitions 302 and 304 which define a chamberwithin which a battery 306 is mounted. The battery provides the powersupply on lines 84 and 86 of the bus for the other units in theassembly. In some arrangements, the battery unit 38 may be omitted byarranging for one or more of the other units such as the actuator 24 tohave an inbuilt battery or to be provided with energy storgage meanssuch as a capacitor for powering the units or to have power supplied bythe controller 14 itself, as on lines 86 and 84 via the lines 20. Thebattery unit 38 has connectors 308 abd 310 to provide interconnectionsof the bus 82 through the unit.

FIGS. 3 and 4 also show the expander unit 40 in more detail. Theexpander unit comprises a tubular housing 312 formed with a spigot 314which can be inserted into the housings of the units 38, 26 and 24 asrequired. The housing has partitions 316 and 318 which define a chamberin which a terminal block 320 is mounted. The partitions also supportconnectors 322 and 324 for the bus 82. FIGS. 3 and 4 also illustrate theconnector unit 42. The unit 42 comprises a tubular housing 328 with aclosed end wall 330. The housing has a partition 332 which defines achamber within which a circuit board 334 is mounted. The partition 332also supports a connector 336. The housing 328 is formed with a spigotportion 338 which is insertable in any one of the units 40, 38, 26 and24 and the arrangement is such that the connector 336 mates with thecomplementary connector of the unit to which it is connected. The unit42 is not however directly insertable in the detonator unit 22.

The circuit board 334 in the unit 42 may comprise a connection blockwhich connects the wires 20 from the controller 14 to the assemblies 6,as in the arrangement shown in FIG. 2. This is the simplest arrangementfor the unit 42.

In another alternative arrangement for the unit 42, the board 334 mayinclude an electronic clock and signal generator to enable activation ofthe actuator unit 24 independently of the controller 14. In thisarrangement (not shown) the clock would control a signal generator whichwould generate signals for actuator unit 24 via the line 88 whichsignals would normally be generated by the controller 14.

In a further alternative arrangement, the unit 42 may include the radiotransceiver 12 which receives signals radiated by the transmitter 15 orthe safety unit 16, as in the arrangement of FIG. 1. In this instance,the lines 340 which comprise the input to the circuitry on the board 334would comprise or be connected to an antenna for receipt of radiosignals.

FIG. 15 illustrates in more detail part of the circuitry for thecontroller 14. The circuitry essentially comprises a microcomputer 342comprising an 8055 CPU 344, a 2716 EPROM 346, an 8155 input/outputdevice 348, a 74123 monostable triggerable multivibrator 352 and a 74377eightbit latch 350. These components are connected together as indicatedby the connection table (FIG. 16) and so that they function as amicrocomputer as is known in the art. The principal function of themicrocomputer 342 is to generate control signals which are used tocontrol the detonator assemblies 6. The microcomputer also interpretsinformation sent to the controller 14 by the various detonatorassemblies 6, input and output to the CPU 344 is via pins 5 and 4respectively. The circuitry includes a keyboard unit 354, the keyboardhaving control switches S1, S2, S3 and S4 which are operated in order toperform various steps required for activation of the detonatorassemblies 6. The microcomputer includes three LED devices 356, 358 and360 which provide a visual indication as to which signals have beendespatched by the computer 342 to the detonator assemblies 6. Theprogrammes for the microcomputer 342 are stored in the EPROM 346.

FIG. 17 is a flowchart illustrating the important programming stepswhich are carried out by the computer 342. On power up, themultivibrator 352 ensures that the CPU 344 is correctly initialised andthe programme waits for one of the control keys S1 to S4 to be actuated,as indicated by step 362. The programme then has four question boxes364, 366, 368 and 370 which determine which if any of the switches S1-S4have been pressed. The switches can be arranged to generate signalswithin the CPU 344 corresponding to different COMMAND signals to betransmitted to the assemblies 6. For instance, the switch S1 can be madeto represent selection of a first BLAST code in which case the CPU 344generates the appropriate BLAST code. The programme then arranges forthe BLAST code to be sent to the detonator assemblies 6, as indicated byprogramme step 372. It follows that those detonators which have thefirst BLAST code will be armed in readiness for operation. After thatsignal is sent, the programme returns to the start. The switch S2 mayrepresent a second BLAST code which will cause a different BLAST code tobe generated by the CPU 444 and sent to the detonator assemblies 6, asindicated by step 374. Those assemblies which have actuator units 24programmed to respond to the second BLAST code will thereby be armed.

The switch S3 if pressed causes the CPU 334 TO generate a signal causingthe armed actuator units 24 to actuate the detonator units 22 connectedthereto. These signals comprise the BOOM command and are distinguishedby the question box 248 in FIG. 9. The despatch of a BOOM command isindicated by programme step 376 in FIG. 13.

The switch S4 represents a reset switch which can be activated by anoperator at any stage during the programme and if pressed a RESETcommand will be generated by the CPU 344, as indicated by step 378.Receipt of a RESET command by the actuator units 24 causes them toreturn to the start of their operating programme, as indicated in FIG.10. The reset signal need not be a specially encoded signal, theactuator units 24 being programmed to automatically reset if any signalsother than known sequence of predetermined commands are received.Resetting the actuators 24 will consequently make the detonator units 22safe so that they cannot be inadvertently exploded. Of course, adetonator unit 22 with fusible links as shown in FIG. 7 cannot reconnectthe fusehead conductors 56 and 58 via the fusible links, but will remainsafe while power is available to maintain the solid state relays 142 and144 on.

The controller programme has a question box 380 which is responsive to amanual or programme generated input to commence calibration procedures.The arrangement shown in FIG. 16 shows a step 382 for generation andtransmission of a CALIBRATE command to start calibration. This commandis the input to box 226 in FIG. 10. The programme then waits for apredetermined period say one second which is accurately known becausecare is taken to ensure that the crystal oscillator 386 and associatedcomponents connected to pins 1 and 2 of the CPU 344 are accuratelyselected whereby the timing of the CPU 344 is accurately known. At theend of the predetermined period, an END calibrate command is generatedas indicated by the step 388. This may be effected by generation of avalid BLAST code. Many variations and enhancements would of course beavailable in the software for the microcomputer 342.

FIG. 18 shows a detonator assembly 434 comprising a detonator unit 22,actuator unit 24 and connector unit 42. In this arrangement theconnector unit 42 is arranged for connection to the controller 14 by theconductors 10 and wires 20, as in FIG. 2. The detonator assembly 434receives power directly from the controller 14 and to be actuated at apredetermined interval after voltage has been disconnected from thewires 20. In a blast using these assemblies, it would not matter if thewire 20 or conductors 10 were broken by actuation of assemblies whichhave been actuated earlier since the assemblies have their own powersupplies and will be actuated at a predetermined period after thevoltage has been disconnected regardless of whether the conductors 10 orwires 20 remain intact.

FIG. 19 illustrates in more detail the circuitry for the actuator uinit24 of assembly 434. The circuitry essentially comprises a microcomputer436 comprising an 8055 CPU 438, a 2176 EPROM 440, an 8155 input/outputdevice 442, a 743123 triggerable multivibrator 444, and a 74377 eightbit latch 446. These components are connected together as indicated bythe connection table (FIG. 20) so that they function as a microcomputeras is known in the art. The principle function of the microcomputer 436is to generate control signals which are used to control the detonatorassembly 436. In this arrangement, the power supply line 84 and groundline 86 are connected to the conductors 10 so as to establish directconnection to the controller 14. The voltage on the power supply line 84charges a storage capacitor 450. The diode 448 ensures that the "powersense"line 5 can detect the discontinuation of power from the controller14 on line 84 even while the capacitor 450 maintains the actuator 436on. The capacitor 450 is chosen so that it will have sufficient chargeto power the circuitry for the microcomputer 436 after the voltagesupply level has been removed from supply line 84. As soon as themultivibrator 444 operates after power on, it will properly initialisethe CPU 438. The input pin 5 of the CPU is connected to the line 84 soas to indicate a "power up". After power up, the microprocessor 436 willoperate to generate an ARM command which is communicated via pins 31 and32 of the unit 472 to the detonator unit 22. The CPU 438 will then waituntil the voltage falls to zero or below a predetermined level on line84, and, after a predetermined period, the fusehead actuating currentwill be generated to initiate the flashing charge 64 via pins 29 and 30to cause activation thereof.

FIG. 21 is a flowchart illustrating the important programming stepswhich are carried out by the microcomputer 436. The programme starts onpower up and then immediately generates an ARM command, as indicated bystep 452, for the detonator unit 22. The ARM command will then wait fora predetermined period say 0.253 seconds before taking any other action.This prevents premature operation of the system as the result oftransients or the like which might occur shortly after power up, kandallows time for mechanical relays in the detonator unit 22 to switch.This step is indicated by programming step 454. The programme then waitsfor the voltage to fall on line 84, as indicated by step 456. When thevoltage on line 84 falls to zero or below a pre-determined level the CPUwill then wait a pre-determined delay so that the detonator assembly 434will be actuated in the correct sequence relative to other assemblies.This is indicated by programming steps 458 and 460 representingretrieval of the delay period from the EPROM 440 and thereafter waitingthe delay period. At the end of the delay period, the programme thencauses generation of the fusehead actuating current for actuation of thedetonator unit 22, as indicated by step 462. The programme then passesto a question box 464 which ascertains whether the programme is stilloperating indicating whether the detonator unit 22 has been successfullyactuated or not. If it has not, it will return to the step 452.

FIG. 22 shows an alternative circuit for use in the actuator unit 24 ofthe assembly 436, shown in FIG. 19. In this arrangement the detonatorassembly 434 is arranged to be actuated a predetermined period afterpower has been applied thereto via the conductors 10 and wires 20 of thearrangement shown in FIG. 2. The circuit of FIG. 22 essentiallycomprises a microcomputer 466 comprising an 8085 CPU 468, a 2176 EPROM470, and 8155 input/output unit 472, a 74123 monostable triggerablemultivibrator 474, and a 74377 eight bit latch 476. These components areconnected together as indicated by the connection table (FIG. 23) sothat they function as a microprocessor as is known in the art. Themicrocomputer has programmes stored in its EPROM 470 for carrying outprimarily the programme shown diagramatically in the flowchart of FIG.24.

On the application of a voltage above a predetermined level, e.g. 2.4volts, on the supply line 84, the multivibrator 474 will reset the CPU468 and various circuit and programming functions are properlyinitialised. The CPU 468 will then start running and its first functionwill be to generate an ARM command on pins 31 and 32 of the unit 472 forthe detonator unit 22. This is indicated by the programming step 478 ofFIG. 24. The programme then waits a fixed delay period as indicated bystep 480. The fixed delay period say 0.25 seconds, is provided so as toprevent inadvertent operation caused by transients or the like whichmight occur shortly after power up, and allow time for relays to switch.All of the detonator assemblies for a particular blast would have thesame fixed delay period. The programme then reads a pre-selected delayfrom the EPROM 470, as indicated by programme step 482. The pre-selecteddelay can be different for particular actuator units 24 so that apredetermined blast sequence can be established. The programme thenwaits for the preselected delay period, as indicated by programme step482 then causes generation of the fusehead actuating current via pins 29and 39 of the unit 472 as indicated by step 486. The BOOM commandappears on pins 29 and 30 of the unit 472. The BOOM command causes thedetonator unit 22 to explode.

If the unit 22 fails to explode, the programme will pass to question box488 which will return the programme to the start if the microcomputer466 has remained in tact.

Many modifications will be apparent to those skilled in the art. Forinstance, integration techniques could be used to integrate circuitswhich are shown in non-integrated form.

I claim:
 1. An actuator for a detonator responsive to at least one inputsignal from a control device comprising:means for inputting apredetermined input signal from said control device, the predeterminedinput signal being a voltage step signal, the leading edge of whichcomprises an arm signal and the trailing edge of which an actuatesignal; means for generating an output arm signal upon input of saidpredetermined input signal to cause said detonator to change from adisarmed state to an armed state in which said detonator is capable ofbeing actuated; and means for generating an output actuate signal tocause an explosive actuation of said detonator a predetermined periodafter the input of said predetermined input signal.
 2. A detonatoractuator system comprising:a control device microcomputer including:amemory that stores an arm code and an actuate code, an arm key, meansfor generating and emitting an arm signal derived from said arm codeupon actuation of said arm key,an actuate key, and means for generatingand emitting an actuate signal derived from said actuate code if saidactuate key is actuated within a first predetermined period afteractuation of said arm key; an actuator for a detonator including:meansfor inputting said arm signal and said actuate signal, means forgenerating an output arm signal upon input of said arm signal to causesaid detonator to change from a disarmed stated to an armed state, andmeans for generating an output actuate signal upon input of said actuatesignal to cause explosive actuation of said detonator a secondpredetermined period after the input of said first predetermined input;and wherein the memory of the control device microcomputer holds a resetcode and includes means for generating an output reset signal thatrenders the detonator incapable of being explosively actuated on failureto actuate the actuate key within the predetermined period afteractuation of the arm key until said output arm and output actuatesignals are received within said predetermined period.
 3. A detonatoractuator system comprising:a control device microcomputer including:amemory that stores an arm code and an actuate code, an arm key, meansfor generating and emitting an arm signal derived from said arm codeupon actuation of said arm key, an actuate key, means for generating andemitting an actuate signal derived from said actuate code if saidactuate key is actuated within a first predetermined period afteractuation of said arm key, and means for generating a calibrate signalupon actuation of one of a calibrate key and a program instruction; anactuator for a detonator including:means for inputting said arm signal,said actuate signal, and said calibrate signal, means for generating anoutput arm signal upon input of said arm signal to cause said detonatorto change from a disarmed stated to an armed state, means for generatingan output actuate signal upon input of said actuate signal to causeexplosive actuation of said detonator a second predetermined periodafter the input of said first predetermined input, means for calibratingsaid second predetermined period on a time basis relative to saidcontrol device, and means for storing said calibrated secondpredetermined period.
 4. A detonator actuating system according to claim3, further including a transducer unit which is couplable to theactuator such that all the appropriate electrical connections are madeby the coupling, the transducer being responsive to a preselectedphysical parameter and being able to generate condition signals relatedto said parameter so as to permit variation of the calibration of theactuator, the variation being communicated to the control device.
 5. Acontrol device microcomputer for use with detonators comprising:a memorythat stores an arm code and an actuate code; an arm key; means forgenerating and emitting an arm signal derived from said arm code uponactuation of said arm key; an actuate key; means for generating andemitting an actuate signal derived from said actuate code if saidactuate key is actuated within a first predetermined period afteractuation of said arm key; and wherein the memory of the microcomputerholds a reset code, and includes means for generating an output resetsignal that renders the detonators incapable of being explosivelyactuated on failure to actuate the actuate key within the predeterminedperiod after actuation of the arm key until said output arm and outputactuate signals are received within said predetermined period.
 6. Acontrol device according to claim 5 wherein the arm signal and actuatesignal from the control device to the actuator is a voltage step signalin which the leading edge of the signal comprises the arm signal and thetrailing edge the actuate signal.